It is built on the Periyar River, in the ravine between the Kuravan and Kurathi Hills in Kerala, India. At 167.68 metres, it is one of the highest arch dams in Asia and third tallest arch dam. It started generating power on 4 October 1975.[1] Technically, the dam type is a concrete double, curvature parabolic, thin arc dam.[2]

This dam was constructed along with two other dams at Cheruthoni and Kulamavu. Together, the three dams have created an artificial lake that is 60 km² in area. The stored water is used to produce electricity at the Moolamattom Power house, which is located inside nearby rocky caves. The Government of Canada aided in the building of the dam with long term loans and grants.[1]

Scenic view of Idukki Reservoir.

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The idea of constructing a dam for power generation was first conceived in 1919. As per history, Shri Kolumban, the head of 'Araya' race during 1922, showed the way to the Malankara Estate Superintendent and his friend AC Thomas Edattu, who were on hunting spree in the forest, the spot of present Arch Dam. He told them of the legend of Kuravan and Kurathi Hills. Mr. Thomas was impressed by the sight of water flow between the mountains and it was his idea that has materialized in the form of Idukki Arch Dam. Sri. W.J.John of Malankara Estate submitted a report to the Government of Travancore in 1932 on the possibility of constructing a dam at Idukki for Power Generation.

In 1947, a preliminary investigation report was prepared and submitted by Sri. P.D. Joseph John, the then Chief Electrical Engineer to the Government of Travancore. It was during 1956 that the Central Water Commission conducted a detailed investigation based on the Government's request. The project report was prepared in 1961 and the Planning Commission accorded sanction for implementing the scheme in 1963 and the preliminary works of the project were started.

The construction of this Dam commenced on 30 April 1969. Storage of water in Idukki reservoir commenced in February, 1973. The inauguration of trial run of the first machine was celebrated on 4 October 1975. Commercial operation of the Power Station was Commissioned on 12 February 1976 by the then Hon. Prime Minister Smt. Indira Gandhi. The Government of Canada aided the Project with long term loans and grants. M/s S.N.C.Inc., Canada, a well-known firm of Consulting Engineers were advising and assisting Project Engineers under the Canadian Aid.

Construction of this Arch Dam and two other dams at Cheruthony and Kulamavu has created an artificial lake of 60 km2 width and the water stored is utilized for production of electricity at the unique Moolamattom Power house, which is located inside the rocky caves.

Idukki Dam is 554 feet tall, constructed between the two mountains - Kuravanmala (839 meters) and Kurathimala (925 meters ). This project is situated in Idukki District and its underground power house is located at Moolamattom which is about 43 km from the dam.

Twice in the past, the shutters had to be opened; during the northeast monsoon (October to December) on both occasions. The first time was in 1981 (when the shutters were repeatedly opened and shut between October 29 and November 13) and the second time was in 1992 (when they were kept open for 12 days from October 12 to 23). On both occasions, the water level in the dam touched the brim only when the storage built up during the southwest monsoon (June to September) was augmented by the inflow received immediately afterwards following heavy downpour early in the northeast monsoon.[3]

Idukki Dam before being filled with water (March 17, 1974. Manorama archive)

The Project harnesses a major portion of the power potential of Periyar, the largest river in Kerala, by the creation of a reservoir of 2,000 M.cum (2 Billion Tonnes) capacity, diversion of waters thus impounded through a water conductor system consisting of a power tunnel and two underground pressure shafts to an underground power house situated in Moolamattom. The installed capacity of the Power House is 780MW consisting of 6 Units of Pelton-type turbines with a power generation capacity of 130 MW each. The regulated waters of Periyar falls through a drop of about 669.2 metres (2195 feet) while generating power in the underground power house.

Irrigation

The tail waters flowing to Kudayathurpuzha through tunnel and open channel is diverted for irrigation purposes in the Muvattupuzha Valley.

Tourist destination and attraction

Earlier, there was a blanket ban on public entry in to the dam due to security reasons. Later, it was relaxed opening the dam for public for 10 days during the Onam and the Christmas seasons. The duration has been increased to one month since last year. Cameras and cell phones are not allowed inside the dam area. The entry fee is Rs.10 for adults and Rs.5 for children. The fee for 15-minute boating service for five persons is Rs. 600.[4]

Idukki valley is 121 km away from Kottayam, and is a small hill town surrounded by a spread of beautiful, wooden valleys and meandering streams. Idukki is a well known tourist center in Kerala.

The Idukki Wildlife Sanctuary extends over the Thodupuzha and Udumbanchola taluks of Idukki district, spread over 77 km2 and is about 450 – 748 m above sea level. The Idukki Reservoir formed by three dams - Cheruthoni, Idukki and Kulamavu - extends to 33 km2. One can find Elephants, bisons, sambars deers, wild dogs, jungle cats, tigers, wild boars etc. and variety of Snakes like Cobra, viper, krait and a number of non poisonous snakes in this Sanctuary. The birds of Idukki are Jungle fowl, myna, laughing thrush, black bulbul, peafowl, woodpecker, kingfisher etc.